EFFECT OF IMPOSED WALL TEMPERATURE OSCILLATIONS ON THE STABILITY OF NATURAL-CONVECTION IN A SQUARE ENCLOSURE

The present numerical study is directed toward buoyancy-driven laminar flows in a two-dimensional square enclosure with differential heating at the vertical walls. The top and bottom walls are insulated. A time -dependent temperature varying sinusoidal perturbation is imposed on t he hot vertical wall. The cold vertical wall is maintained at a consta nt temperature. The fluid is air with a Prandtl. number of 0.72. Compu tations were carried out at one imposed frequency, which is of the sam e order as the first natural frequency of the system. It was found tha t the perturbations destabilized the pow in that higher amplitudes lea d to lower critical Rayleigh numbers for the pow transitions. Computat ions spanned four regimes: periodic, quasi-periodic with two frequenci es, quasi-periodic with three-frequencies, and chaotic.